Improved enzymatic properties of Candida rugosa lipase immobilized on ZnO nanowires/macroporous SiO2 microwave absorbing supports

•ZnO nanowires/SiO2 composites were used as a microwave absorbing support to immobilize lipase.•The support is easily to be recovered by calcination.•The microwave absorbing properties of ZnO nanowires were proved to be helpful for the synergistic effect.•The immobilized lipase exhibited relatively high thermal stability and activity under MW.•The immobilized lipase was used to catalyze synthesis of phytosterol esters under MW.

ZnO nanowires/macroporous SiO2 composites were used as a new type of microwave absorbing support to immobilize Candida rugosa lipase (CRL). Under microwave irradiation the immobilized lipase was used to catalyze esterification of phytosterol and oleic acid for the synthesis of phytosterol esters. A great improvement of the catalytic activity was found in the systems in which composited ZnO nanowires were present. The microwave absorbing properties of ZnO nanowires have been proved to be helpful for the synergistic effect between microwave irradiation and enzyme catalysis. The immobilized CRL showed higher thermal stability at 55 °C under microwave irradiation than conventional heating. A maximum molar conversion of 95.4% under microwave irradiation was achieved under the optimal condition: 0.1 M phytosterol, 0.2 M oleic acid, water activity (aw) of 0.11, reaction temperature at 50 °C and reaction time of 1 h.

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